A swashplate or swash plate is a component which can be used to convert circular motion into reciprocating motion, and vice versa. Swashplates can be used in a variety of settings, with one of the most famous applications being the helicopter swashplate, which is used by the pilot to adjust the blades of a helicopter in order to achieve lift and control the position of the helicopter. Certain mechanical pumps and grinders may also utilize swashplates.

The basic swashplate mechanism includes a disc which is fixed to a shaft, so that the disc rotates with the shaft. When the disc is straight, nothing appears to be happening, but when it is angled, the turning of the shaft causes the disc to appear to oscillate as it moves around. A secondary plate mounted in a stationary position below the first plate will change angles as the angled rotating plate moves over it, turning the circular motion of the shaft into reciprocating motion in shafts mounted to the stationary plate.

This basic engineering trick can be utilized in a wide variety of settings, in mechanisms which vary in size from tiny components in toy cars to huge machines in factories. Large or small, a swashplate will work in the same way, and when it is calibrated properly, it can produce seamless, very efficient conversion of different types of motion.

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One example of a way in which a swashplate can be moved is in a car, where pistons move up and down as they are fired by the engine. The reciprocal motion of the pistons can be converted into circular movements which will rotate the axles with the use of a swashplate. In this case, the firing pistons would push against the stationary plate, causing it to press against the fixed plate and rotate the shaft. To slow or speed the amount of rotation, the firing interval of the pistons could be altered.

In helicopters, the swashplate mechanism is used to allow the pilot to adjust either one blade at a time, or all of the blades, to create different angles. These angles are used to generate lift as the aircraft spins, and to change the position of the aircraft once it is airborne. Blade control can be either cyclic or collective. In cyclic blade control, a single blade is adjusted with the use of a fixed outer ring. Collective blade control moves both the fixed outer ring and the rotating inner ring to adjust all of the blades at once.

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